One class of compounds finding increasing use in chemical vapor deposition of electrically conductive metals and metal compounds are organometallic precursors. An example organometallic precursor is Ti(N(CH.sub.3).sub.2).sub.4, named tetrakisdimethylamido titanium (TDMAT). Organometallic compounds contain a central or linking atom or ion (Ti in TDMAT) combined by coordinate bonds with a definite number of surrounding ligands, groups or molecules, with at least one of such being organic (the (N(CH.sub.3).sub.2 groups in TDMAT). The central or linking atom as accepted within the art may not be a "metal" in the literal sense. As accepted within the art of organometallic compounds, the linking atom could be anything other than halogens, the noble gases, H, C, N, O, P, S, Se, and Te.
An example chemical vapor deposition process is the reaction of TDMAT with nitrogen (either as N.sub.2 or NH.sub.3) in the presence of a carrier gas to produce TiN. Hydrogen is sometimes also utilized as a reactant gas to facilitate reaction of carbon containing radicals into stable gaseous compounds which are expelled from the reactor. An alternate process combines TDMAT and hydrogen in a plasma chemical vapor deposition reactor to deposit an elemental Ti layer on a substrate.
The above and other chemical vapor deposition reactions involving organometallics are typically conducted at low pressures of less than 1 Torr. It is typically desirable in low pressure chemical vapor deposition processes to operate at as low a pressure as possible to assure complete evacuation of potentially undesirable reactive and contaminating components from the chamber. Even small amounts of these materials can result in a significant undesired increase in resistivity. For example, oxygen incorporation into the film before and after deposition results in higher resistivity. Additionally, it is believed that organic incorporation (specifically pure carbon or hydrocarbon incorporation) into the resultant film reduces density and increases resistivity. Such organic incorporation can result from carbon radicals from the organic portion of the precursor becoming incorporated into the film, as opposed to being expelled with the carrier gas. Carbon incorporation can also cause other undesired attributes in the deposited film, such as low density and poor long term reliability. Although provision of available hydrogen within the reactor is intended to restrict carbon incorporation in the resultant film, unacceptable levels of incorporated carbon typically still result.
It would be desirable to improve upon these and other prior art chemical vapor deposition processes in producing layers having minimal incorporated carbon.